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Category Sulfosalt mineral
(repeating unit)
Strunz classification 2.HC.05a
Crystal system Monoclinic
Crystal class Prismatic (2/m)
(same H-M symbol)
Space group P21/a
Unit cell a = 20.17, b = 7.94
c = 8.72 [Å]; β = 101.12°; Z = 8
Color Grayish black; white with reddish internal reflections in polished section
Crystal habit Acicular crystals and anhedral grains
Twinning Polysynthetic twinning on {100}
Cleavage Perfect on {001}
Fracture Conchoidal
Tenacity Very brittle
Mohs scale hardness 4
Luster Metallic
Streak Brown
Diaphaneity Opaque
Specific gravity 5.2
Pleochroism Relatively strong
References [1][2][3]

Guettardite is a rare arsenic-antimony lead sulfosalt mineral with formula Pb(Sb,As)2S4. It forms gray black metallic prismatic to acicular crystals with monoclinic symmetry. It is a dimorph of the triclinic twinnite.

Discovery and occurrence[edit]

It was first described in 1967 for an occurrence in the Taylor Pit, Madoc, Hastings County, Ontario, Canada. It was named for French naturalist Jean-Étienne Guettard (1715–1786).[1]

It occurs in hydrothermal veins within marble at the type locality in Modoc. It occurs associated with pyrite, sphalerite, wurtzite, galena, stibnite, orpiment, realgar, enargite, tetrahedrite, zinkenite, jordanite, bournonite, sterryite, boulangerite, jamesonite and sartorite at Madoc.[2]

In addition to the type locality, it has been reported from the Brobdingnag mine, near Silverton, Colorado; the Jas Roux deposit in Hautes-Alpes, France; from various marble quarries near Seravezza, Tuscany, Italy; a marble quarry in Valais, Switzerland and from Khaydarkan, Fergana Valley, Alai Mountains, Kyrgyzstan.[1][2]


External links[edit]